Laterally expandable cage

ABSTRACT

A laterally expandable spinal implant includes a central body and two wings that are adapted to be received within an inner chamber formed within the central body. The wings have guide rails that fit into grooves defined in the central body. To ensure that the implant is properly secured, each guide rail has an outer end with a cutting surface that cuts into vertebral end plates when the wings are extended. The two wings are connected together through a central turnbuckle shaft that has geared teeth and threading on both ends that engage threaded cavities in the wings. Through the gear teeth, the turnbuckle shaft is able to be rotated so as to laterally extend the wings from the central member. A locking mechanism locks the turnbuckle shaft to prevent the wings from retracting.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/285,723, filed Nov. 1, 2002 now U.S. Pat. No. 6,723,126,which is hereby incorporated by reference in its entirety.

BACKGROUND

The present invention generally concerns spinal implants, and morespecifically, but not exclusively, concerns a laterally expandablevertebral implant.

A major cause of persistent, often disabling, back pain can arise bydisruption of the disc annulus, chronic inflammation of the disc, orrelative instability of vertebral bodies surrounding a given disc, suchas might occur due to a degenerative disease. In the more severe cases,some form of mechanical limitation to the movement of the vertebrae oneither side of the subject disc is necessary. In such cases, the disctissue is irreparably damaged, thereby necessitating removal of theentire disc. However, when the disc nucleus is removed withoutsubsequent stabilization the same disabling back pain often reoccurs dueto persistent inflammation and/or instability.

Various approaches have been developed to stabilize the adjacentvertebral bodies following excision of this material. In one approach,two adjacent vertebrae are fused together through a fusion device thatis implanted between the vertebrae. Many of these existing implantdesigns have drawbacks that lower the spinal fusion rates. Among thesedesign drawbacks, one such flaw is that the implants subside into thevertebral end plates, thereby reducing the spacing between the vertebralbodies. With prior fusion devices, and even some prosthetic devices, alarge portion of the load is placed against the weakest part of thevertebral body, which can lead to cavitation of the device into thesurrounding vertebral endplates with subsequent collapse of the innerdiscal space and even damage of the vertebrae itself. Another frequentcause for subsistence is created by having a small area of contactbetween the implant and the endplates. As one should appreciate, theless surface area of contact between the implant and the end plates, thegreater the risk of subsistence.

Another flaw of many implants is the lack of stability created afterimplantation. Stability is crucial to the success of a fusion. Theimplant must be securely fixated to the vertebral bodies in order toensure that no movement occurs between the two. If movement does occurbetween the vertebral bodies and the implant, the bone may not properlyfuse, thereby creating stability problems. Moreover, some designs limitthe amount of graft material, which may be able to be used with theimplant. The larger area of graft material that is able to contact theendplates, the better chances of a good, solid bone growth between thetwo vertebrae.

Some designs have created implants in which the majority of the implantis positioned over the harder cortical bone of the apophyseal ring ofthe vertebrae in order to reduce the chances of subsistence. However,with these designs, the implant is made from multiple separatecomponents that are individually assembled together within the discspace. Each component is implanted separately and then attached to oneanother within the disc space. As should be appreciated, assembling suchan implant in the disc space can be rather difficult. Such implants alsotend to lack a stiff central body, which is essential to the stabilityof the implant as well as entire fusion construct. Moreover, suchimplants have no mechanism to fix the implant to the vertebral body.Typically, one has to use bone screws to secure the implant to thevertebral bodies, which makes the implantation process more complicatedand difficult. In addition, such implants generally have a singlelateral width, and therefore, it is generally very difficult, if notimpossible, to adjust for differently sized vertebrae. Another flaw isthat these designs typically do not provide a mechanism for ensuringthat the spacers are properly positioned. Since the lateral spacers ofthese types of implants are independently assembled within the discspace, the lateral members can be positioned at unequal positions alongthe apophyseal ring, thereby increasing the risk that the implant willsubside into the vertebral end plates.

SUMMARY

In one aspect, a spinal implant includes a cage defining an interiorcavity and an expansion mechanism received in the cavity of the cage. Apair of wings are operatively coupled to the expansion mechanism, andthe wings each have opposing vertebrae engaging surfaces that areconfigured to engage opposing vertebrae. The expansion mechanism isoperable to laterally move the wings between the vertebrae from acompact configuration in which at least a majority of the wings arereceived in the cavity of the cage to an expanded configuration in whichthe wings extend from the cage with the vertebrae engaging surfaces oneach of the wings engaging the vertebrae.

Another aspect concerns a fusion device for implanting between opposingvertebrae that define a disc space. The device includes a central memberand at least one pair of lateral members slidably coupled to the centralmember. The device further includes means for extending the lateralmembers from the central member into the disc space between thevertebrae with each of the lateral members engaging both of thevertebrae.

In a further aspect, an apparatus includes a spinal implant. The spinalimplant includes a central member defining an interior cavity and a pairof openings defined on opposite sides of the central member that openinto the interior cavity. A pair of wings are slidably received in theopenings in the central member. A shaft is coupled to the wings, and theshaft has at least one threaded portion threadedly engaging at least oneof the wings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top perspective view of a spinal implant according to oneembodiment in an expanded configuration.

FIG. 2 is an exploded view of the FIG. 1 implant.

FIG. 3 is a top perspective view of the FIG. 1 implant in a compactconfiguration.

FIG. 4 is an end view of the FIG. 1 implant in a compact configuration.

FIG. 5 is a top perspective view of the FIG. 1 implant in an expandedconfiguration.

FIG. 6 is an end view of the FIG. 1 implant in an expandedconfiguration.

FIG. 7 is a perspective view of the FIG. 1 implant attached to aninserter tool.

FIG. 8 is an enlarged, perspective view of the FIG. 1 implant coupled tothe FIG. 7 tool.

FIG. 9 is a partial cross-sectional view of the FIG. 1 implantpositioned in an interdiscal space in an expanded configuration.

FIG. 10 is a side view of the FIG. 1 implant in the interdiscal space.

FIG. 11 is a top view of the FIG. 1 implant in the interdiscal space.

FIG. 12 is a perspective view of a spinal implant according to anotherembodiment.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent invention, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is intended thereby. Any alterations andfurther modification in the described processes, systems, or devices,and any further applications of the principles of the invention asdescribed herein are contemplated as would normally occur to one skilledin the art to which the invention relates. Some embodiments of theinvention are shown in great detail, although it will be apparent tothose skilled in the relevant art that some of the features may not beshown for the sake of clarity.

A laterally expandable spinal implant 100 according to one embodiment ofthe present invention will now be described with reference to FIGS. 1-6.As shown in FIGS. 1 and 2, the implant 100 includes a central member orcage 102, a pair of lateral members or wings 104 that are adapted tolaterally extend from the cage 102, and an expansion mechanism 106 (ormeans) that is operable to extend the wings 104. In the illustratedembodiment, the expansion mechanism 106 includes a turnbuckle orthreaded shaft 108 that connects the wings 104 together. In otherembodiments, the expansion mechanism can include hydraulic pistons,mechanical linkages, and the like. The shaft 108 includes a gear 110that is centrally located on the shaft 108 between opposing threadedportions 112 and 114. In one embodiment, threads 116 on the threadedportions 112 and 114 are oppositely threaded (i.e., one is a left handedthread and the other is a right handed thread.) In one form of thepresent invention, the threads 116 of the threaded portions 112 and 114have an equal pitch such that the wings 104 are able to extend from thecentral member 102 at the same rate. This ensures that the implant 100has a symmetrical configuration, which in turn aids in centering theimplant 100 over the vertebrae. The threaded portions 112 and 114threadedly engage threaded openings 118 that are defined in each of thewings 104. In another embodiment, only one end of the shaft 108 isthreaded, while the other end of the shaft 108 is unthreaded. With thisembodiment, the wings 104 are still extended by rotating the shaft 108.

Implant 100 further includes a lock mechanism 120 that is used to lockthe wings 104 in an expanded configuration in which the wings 104laterally extend from the cage 102. In the embodiment illustrated inFIG. 1, the lock mechanism 120 includes lock cavities 122 that aredefined in each of the wings 104 next to the threaded openings 118. Asillustrated in FIG. 2, the lock cavities 122 open into the threadedopening 118 in the wings 104. In one embodiment, each lock cavity 122 isonly partially threaded such that once the wings 104 are in the expandedconfiguration, the shaft 108 can be slid from the threaded opening 118into the lock cavity 122. By being only partially threaded near theentrance of the cavity 122, the shaft 108 is unable to rotate such thatthe wings 104 are unable to be retracted. In another embodiment, thelock cavity 122 is unthreaded, but has a depth shallower than thethreaded openings 118 so as to keep the wings 104 in the expandedconfiguration, when the shaft is moved into the lock cavities 122.

Referring to FIG. 2, each wing 104 includes opposing vertebrae engagingsurfaces 202 that are configured to engage opposing vertebrae, as wellas medial 204 and lateral 206 side surfaces. As shown, the wings 104,according to the illustrated embodiment, have a generally tapered shapeso as to coincide with the vertebral endplate geometry. The vertebraeengaging surfaces 202 generally taper from the medial sides 204 to thelateral sides 206. To further reduce trauma upon insertion of theimplant 100, the wings 104 have beveled edges 208 between the vertebraeengaging surfaces 202 and the lateral surfaces 206. In the illustratedembodiment, the medial sides of the wings 104 are generally flat so asto allow the wings 104 to contact one another in a compact state whenthe wings 104 are retracted within the cage 102. The medial sides 204 ofthe wings 104 define access channels 210 around the threaded opening 114and the lock cavity 122. In one form, access channel 210 is sized toreceive the gear 110 on the shaft 108. The access channel 210 has anopening 212 that allows the physician to gain access and rotate the gear110 so as to expand the implant 100. In the illustrated embodiment, thelateral sides 206 have a generally curved shape in order to coincidewith the shape of the apophyseal ring of the vertebrae.

With continued reference to FIG. 2, the cage, 102 has a proximal or toolengaging end wall portion 214, an opposite distal end wall portion 216,and a pair of opposing lateral wall portions 218 that together define aninterior cavity 220. The cage 202 further has a pair of opposingvertebrae engaging surfaces 222 that are configured to engage opposingvertebrae. To coincide with vertebrae geometry, surfaces 222 in theillustrated embodiment are tapered such that surfaces 222 angle towardsone another from the proximal end wall portion 214 to the distal endwall portion 216. As shown, the interior cavity 220 extends through bothvertebrae engaging surfaces 222. In the illustrated embodiment, the cage102 has a generally rectangular shape. The vertebrae engaging surfaces222 can include texturing so as to prevent expulsion of the implant 100from the vertebrae. For instance, the vertebrae engaging surfaces 222 inthe illustrated embodiment have ridges 224 that aid in preventingexpulsion of the implant 100. As should be appreciated, in other formsof the present invention, the vertebrae engaging surfaces 222 caninclude other types of texturing for preventing expulsion of the implant100. The proximal end wall portion 214 defines a tool opening 226through which an insertion tool can be inserted into the interior cavity220, and lateral walls 218 define wing openings 228 through which thewings 104 are slidably received into the interior cavity 220.

FIGS. 3 and 4 illustrate the implant 100 when in a compact state inwhich the wings 104 are retracted inside the interior cavity 220. Asshown in FIG. 3, the wings 104 have one or more guide rails 302 thatengage corresponding guide channels 304 formed around the wing openings228. In the illustrated embodiment, each wing 104 has four guide rails,with a pair positioned along each opposing vertebrae engaging surface202 of the wing 104. In order to provide further stability, the guiderails 302 and the corresponding channels 304 in the illustratedembodiment have a general dovetail shape. Moreover, as discussed infurther detail below, the dovetail shape of the guide rails 302 ensurethat the wings 104 remain secure in the vertebrae once implanted. Whenthe implant 100 is in a compact state, the majority of the wings 104 arereceived in the interior cavity 220 of the cage 102. In the compactstate, the medial sides 204 contact each other and the entrances 212 ofthe access channels 210 define an access opening 306 through which aninsertion tool can gain access to gear 110 on shaft 108 in order torotate the shaft 108.

As previously mentioned, the gear 110 is used to rotate the shaft 108,thereby causing the wings 104 to extend from the cage 102. FIGS. 5 and 6show the implant 100 with the wings 104 in a laterally expanded state inwhich the wings 104 extend from the cage 102. As should be appreciated,the expansion mechanism 106 allows the wings 104 to extend at varyingdistances from the cage 102 such that the size of the implant 100 can beadjusted to correspond to the size of the selected vertebrae. As shownin FIG. 6, outer lateral ends 402 of the guide rails 302 define aninward notch 404 such that the outer lateral ends 402 form cutting edges406. As the wings 104 are extended, the cutting edges 406 cut channelsinto the vertebrae. The cutting edges 406 act like spikes to embed thewings 104 into the vertebral endplates. Once the wings 104 are extended,the dovetail shape of the guide rails 302 help to ensure that the wings104 are firmly secured to the vertebrae. Once the wings 104 are in thedesired extended position, the shaft 108 is then slid into the lockcavity 122 (FIG. 2) in order to lock the wings 104 in the desiredextended position. After implantation, bone graft material can be packedinto the interior cavity 220 via tool opening 226 to promote fusion ofthe vertebrae. With the wings 104 slightly extended, bone graft materialcan even be packed before implantation. Following implantation, theinterior cavity 220 provides a large area in which a fusion mass can beformed between the vertebrae.

An implant inserter assembly 700 that includes the implant 100 coupledto an inserter 702 according to one embodiment of the present inventionis illustrated in FIGS. 7 and 8. The inserter 702 includes a drivinghandle 704, an actuation knob 706, a shaft portion 708, a gripping knob710 and a head portion 712. In the illustrated embodiment, the handleportion 704 is solid and includes an impaction surface 714 against whicha hammer or the like can strike to drive implant 100 between thevertebrae. The actuation knob 706 is connected to a drive shaft 802,which extends from the actuation knob 706, through the shaft 708, andthrough the head 712. When the implant 100 engages the inserter 702, theactuation knob 706 is able to extend the wings 104. As shown in FIG. 8,the drive shaft 804 has at one end a drive gear 804 with teeth 806 thatengage an intermediate gear 808 that is coupled to the head 712 througha carrier member 810. During implantation, the intermediate gear 808engages gear 110 on the shaft 108 of the implant 100. As the actuationknob 706 is rotated, the drive shaft 802 rotates drive gear 804. Inturn, the drive gear 804 rotates the intermediate gear 808, which thenis used to rotate the shaft 108 in order to extend the wings 104. Thegripping knob 710 is rotated in order to extend gripping fingers 812inside the interior cavity 220 such that the inserter 702 engages thetool opening 226 of the implant 100. The gripping knob 710 and thegripping fingers 812 can be optional, such that in one embodiment knob710 and fingers 812 are not included. To provide a large surface areafor impaction, the head 712 has a generally rectangular shape togenerally coincide with the shape of the proximal end wall portion 214of the implant 100.

FIGS. 9, 10 and 11 show various views of the implant 100 when implantedbetween adjacent vertebrae 902 and 904. Before implantation, a portionof the annulus is removed to create a larger disc space for theimplantation of the implant 100. The vertebral end plates are preparedby removing cartilaginous material connected to them. A window 906,which generally corresponds in shape and size to the cage 102, is formedin both vertebrae 902 and 904. Before implantation, the wings 104 arepositioned in their retracted position inside the interior cavity 220 ofthe implant 100, and the implant 100 is attached to the inserter 702 inthe manner as illustrated in FIG. 7. The implant 100 is then impactedinto the window 906 formed between vertebrae 902 and 904. Rotation ofthe actuation knob 706 on the inserter 702 causes the shaft 108 on theimplant 100 to rotate, thereby expanding the implant 100. As previouslymentioned, this causes the wings 104 to laterally expand from the cage102 between the vertebrae. In one embodiment, the wings 104 are extendedfrom the cage 102 at the same rate to ensure that the implant 100remains centered between the vertebrae 902 and 904. As the wings 104extend, the cutting edges 406 of the guide rails 302 cut into thevertebrae 902 and 904, thereby ensuring that the implant is securelyfastened to the vertebrae 902 and 904. The wings 104 are expanded untilthey are positioned over the apophyseal ring, which contains the hardercortical bone. As shown in FIG. 9, the shape of the wings 104 generallycorrespond to the geometry of the end plates of vertebrae 902 and 904.Due to the large surface area provided by the implant 100 and by beingsupported on the harder cortical bone of the apophyseal ring, the riskof subsidence of the implant 100 into the vertebrae 902 and 904 isreduced. Moreover, the construction of implant 100 allows for theimplant to have variable dimensions such that the implant 100 canaccommodate vertebrae of varying sizes. Once the implant 100 has beenexpanded to the desired expansion configuration, the turnbuckle 108 canbe moved into the block cavity 122 such that the wings 104 are lockedinto position.

Referring to FIG. 12, an implant 1200 according to another embodiment ofthe present invention incorporates a number of the same featuresdescribed above, with the exceptions noted below. As should beappreciated, the locking mechanism 120 in this embodiment differs fromthe one described above. In the embodiment illustrated in FIG. 12, thelocking mechanism 120 includes a leaf spring 1202 that is attached tothe distal end wall portion 216 of the cage 102. As shown, the leafspring 1202 engages the gear 110 on the shaft 108. The leaf spring 1202is positioned such that the shaft 108 can only be rotated in onedirection so that the wings 104 can only move in a laterally expandingdirection. The spring 1202 resists rotation of the shaft in the oppositedirection, so that once the wings 104 are extended to the desiredlocation the spring 1202 locks the wings 104 into position.

While specific embodiments of the invention have been shown anddescribed in detail, the breadth and scope of the present inventionshould not be limited by the above described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents. It is understood that only selected embodiments have beenshown and described and that all changes and modifications that comewithin the spirit of the invention are desired to be protected.

1. A spinal implant, comprising: at least two lateral members, said lateral members each being shaped to engage apophyseal rings of opposing vertebrae when said lateral members are in an extended configuration, said lateral members each having a lateral side with a curved shape that coincides in shape to the apophyseal rings; and a expansion mechanism coupled to said lateral members to extend said lateral members away from one another into said extended configuration at which said lateral members engage the apophyseal rings of the opposing vertebrae.
 2. The implant of claim 1, wherein said expansion mechanism includes a shaft having threaded portions on opposite ends that threadedly engages said lateral members.
 3. The implant of claim 2, wherein said threaded portions are oppositely threaded and have equal thread pitch.
 4. The implant of claim 1, further comprising a lock mechanism operable to lock said lateral members in said extended configuration.
 5. The implant of claim 4, wherein said lock mechanism included lock cavities constructed and arranged to lock said lateral members in said extended configuration.
 6. The implant of claim 4, wherein said lock mechanism includes a leaf spring.
 7. The implant of claim 1, wherein at least one of said lateral members has a guide rail.
 8. The implant of claim 7, wherein said guide rail has a dovetail cross-sectional shape.
 9. The implant of claim 7, wherein said guide rail has an outer cutting edge constructed and arranged to cut the vertebrae during extension of said wings.
 10. The implant of claim 1, further comprising a cage in which said lateral members are received.
 11. A spinal implant, comprising: at least two lateral members, said lateral members each being shaped to engage apophyseal seal rings of opposing vertebrae when said lateral member are in an extended configuration; a expansion mechanism coupled to said lateral members to extend said lateral members away from one another into said extended configuration at which said lateral members engage the apophyseal rings of the opposing vertebrae; wherein said expansion mechanism includes a shaft having threaded portions on opposite ends that threadedly enagaes said lateral members; and wherein said shaft includes a gear positioned between said threaded portions for rotating said shaft.
 12. A method, comprising: inserting a spinal implant in a compact configuration between opposing vertebrae that have apophyseal rings, wherein the implant has an expansion mechanism coupled between at least two wings; and expanding the wings from one another in a lateral direction between the opposing vertebrae with the expansion mechanism to an expanded configuration at which the wings each engage the apophyseal rings of both the vertebrae.
 13. The method of claim 12, wherein: the expansion member includes a threaded shaft; and said expanding includes rotating the threaded shaft.
 14. The method of claim 12, further comprising locking the wings in the expanded configuration.
 15. The method of claim 14, wherein: the expansion member includes a shaft with a gear; the implant includes a leaf spring; and said locking includes engaging the leaf spring with the gear.
 16. The method of claim 14, wherein: the expansion member includes a shaft; the lateral members have lock cavities; and said locking includes sliding the shaft into the lock cavities.
 17. The method of claim 12, further comprising: securing the spinal implant to a spinal inserter prior to said inserting.
 18. The method of claim 17, wherein said expanding includes expanding the wings with the inserter. 